1. Field of the Invention
This invention relates to the field of apparatus for applying joint tape and adhesive over the joints between wallboard sections.
2. Description of Prior Art
The Automatic Wallboard Joint Taper shown in Hauk and Konishi U.S. Pat. No. 4,090,914 has proven to be a significant improvement over previous tape and adhesive applicators, due to its time, labor and maintenance-reducing features as well as its smooth and efficient operation. However, a limitation is present in such taper (and other tapers) which, at least potentially, can hinder its normally very efficient and trouble-free operation.
The limitation lies in the nonadjustable ratchet mechanism associated with the taper's toothed traction or drive wheels which engage and roll along the wallboard as the taper is used. This mechanism comprises a generally straight wire spring fixed at one end to a side plate of the taper's head assembly and having a small pawl wedge fixed to its free end. The cantilevered spring is shaped and positioned to bias the wedge into a locking position between the teeth on one of the traction wheels and a knife-guiding tube behind such wheel to preclude rotation of the wheel in one direction. Upon a rotation of the wheel in the opposite (or "operating") direction, the wedge is cammed repetitively by the wheel teeth away from its locking position against the biasing force of the cantilevered spring to which it is attached. This camming action imposes a constant, though relatively small, "tensioning" force on the rotating traction wheel, slightly restraining its rotation in such operating direction.
It has been found that although the described ratchet mechanism works quite well, many workmen using the taper on a day-to-day basis develop a preference for a greater or smaller tensioning force. To achieve this result, they commonly attempt to bend the straight pawl spring, to increase or decrease its biasing force, by inserting a screwdriver or other tool into the taper head. This may break the spring, requiring installation of a new spring and wedge. Because of the configuration and location of the present ratchet mechanism, such replacement is not an easy task, requiring disassembly of at least a portion of the multi-component taper head, and, thus, a significant amount of down time.
Additionally, these attempts to adjust the nonadjustable frequently render the present ratchet mechanism inoperable, even if the workman manages to only bend the spring with his screwdriver. This is due to the fact that, despite their simple appearance, the pawl wedge and its spring must be manufactured and positioned relative to the drive wheel teeth and knife tube with a relatively great degree of precision to function properly. More specifically, the installed spring must be angled relative to the knife tube in such manner that the spring not only biases the wedge upwardly into engagement with the wheel teeth, but presses the wedge rearwardly against the knife tube as well. Only the most skillful in-field spring bending avoids disturbing this precise angular relationship and rendering the ratchet mechanism inoperative. Of course, such requisite precision also increases the manufacturing, assembly and repair costs of the present ratchet mechanism.
Accordingly, it is an object of this invention to eliminate or minimize above-mentioned and other problems and limitations, while at the same time giving each operator the option to achieve any adjustment he desires.